The present invention relates to a bicycle, and more particularly, to an adjustable pedal driving device for a bicycle which can extend, upon running, the distance between the pedal and the power transmitting axle of a chain sprocket, which transmits the rotating force of the pedals to a rear wheel. Maximum running energy with minimum driving energy consumption can thus be achieved.
Generally, existing bicycles have been designed to have a fixed crankshaft distance between pedal arms and pedals and therefore, its running force depends only upon the driving force of the pedals assembled with the pedal arms. Under such a driving structure of the bicycle, since the rotating force of the pedals is exerted within a predetermined rotary radius, the bicycle requires a lot of driving energy when running on an upwardly inclined road.
To improve this problem as well as to use one""s driving energy effectively, various kinds of pedal mechanisms for varying the length of the pedal arms have been developed.
U.S. Pat. No. 6,152,472 discloses a variable pedal driving device for a bicycle allowing the bicycle pedals to slide along pedal arms utilizing an eccentric member. U.S. Pat. No. 5,207,119 shows two parallel pedal arms mounted on a case where a pair of sun gears are tooth-coupled to an adjacent planetary gear.
Other various kinds of pedal mechanisms for varying the length of the pedal arm have been disclosed for generating maximum torque in the region of the power stroke while in continuous pedaling.
Although various kinds of structures have been considered, there still exists a number of problems. Among the problems is the xe2x80x9cDead Spotxe2x80x9d phenomenon which causes a deterioration in the efficiency of continuous pedaling and smooth pedaling.
The so called xe2x80x9cDead Spotxe2x80x9d, where the efficiency of the torque almost vanishes, occurs with a pedal location in the top position of the cycling path, especially when a rider of a bicycle pushes vertically downward in a vertical direction.
Due to the symmetrical location of bicycle pedals and the elliptical trace of pedaling under conventional variations of the pedal arms, the upper pedal located on the dead spot tends to be placed in a slightly behind position compared with a vertical reference line, which may cause a slight distortion of the rider""s body in a backward direction in order to continue the pedaling process.
In addition to the problem related to the dead spot, the frictional loss or the distortion of the pedal arms of the prior art also hinders the length varying embodiment of pedaling to the actual application of a bicycle.
A general object of the present invention is to provide a variable pedal driving device for a bicycle which can enable pedal arms on which pedals are installed to enlarge the rotary radius of the pedals, where running, thus obtaining optimum driving energy at the expense of minimum physical energy consumption, so that when a bicycle runs in an upward climbing state or for a long distance, fatigue to a user is substantially reduced.
Specifically, the present invention is directed to providing a new pedal mechanism for eliminating the dead spot by synchronizing the generation of maximum torque in the residual moment of rotational inertia in connection with the rotary gear even though the external torque of the pedal arm exerted by an operator vanishes.
Another embodiment of the present invention provides a stable structure of the guide member for the successive motions of pedal arms. The guide member for the driving arm is devised so as to minimize the frictional losses of linear motion and the distortion or the stress exerted by the rotational motion of the pedal arm.
The structure of the pedaling mechanism under the present invention is characterized in that a joining line formed by the tooth-coupling of a fixing gear and a rotary gear is always set to meet with the axle line of a driving arm at a right angle, and the trace of linkage formed by a connection arm and a connection link is set to move as a spiral motion forced to rotate with respect to the center of the fixing gear.